The invention relates to a multi-layer body, in particular in the form of a transfer film, a laminating film, a packaging film, a decoration element or security element, as well as a process for producing such a multi-layer body.
Security documents with a diffractive security element are known for example from EP 0 105 099 B1 and EP 0 375 833 B1. In these security elements, diffraction gratings are moulded into a layer of a multi-layer body and overlaid with a metallic reflective layer. The diffraction of the incident light at these diffraction gratings generates an optically variable effect which is determined by the spatial frequency of the diffraction gratings as well as their azimuthal angle. Thus, in the security element described in EP 0 105 099 B1 the diffraction structure is formed such that the colour pattern arising with a given illumination and viewing direction moves at a locally predetermined speed in a predetermined path when the substrate is rotated in its plane in a given direction of rotation and at a given speed. In EP 0 375 833 B1, the various fields of a grid field with a maximum dimension of less than 0.3 mm are overlaid with different diffraction gratings, with the result that when the security element is viewed different representations occur in different viewing directions of the security element.
A further possibility for producing an optically variable effect is described in WO 03/095657 A2. An achromatic surface structure here is combined with a thin-film structure in overlapping manner. The achromatic structures here have an order of magnitude in which diffraction phenomena influence the optical properties only slightly and thus the structures act essentially like tilted mirrors. The described security element here has partial surfaces which are overlaid with different achromatic surface structures, for example sawtooth structures which, in a first partial surface, have an azimuthal angle different from that of a second partial surface. These different partial surfaces are furthermore additionally overlaid with a thin-film layer structure, with the result that different colour and contrast changes are generated in the partial surfaces and the impression of a defined, almost discrete colour change forms for the observer during rotation or tilting.